This invention relates in general to the mounting of chips to circuit boards, and in particular to mounting chips to microstrip boards.
Integrated circuit semiconductor chips, or simply chips, are mounted to microstrip boards as a means of connecting the chips to other chips and to other electronic devices. A common means of mounting chips to boards is to simply bond them to an upper surface of the board. The chip is electrically connected to ground by providing a copper sleeve down a hole, also known as a via, from the surface to the ground plane. That approach risks introducing a discontinuity of the ground plane that is inadequate for some applications. Such an application is the use of ground vias for connecting a monolithic chip employed at high microwave and millimeter wave frequencies. At such frequencies, the vias act as inductors, resulting in an effective discontinuity in the ground connection. Surface mounting is further disadvantageous in that it results in the chip being vulnerable to being damaged by handling of the assembled boards.
It is desired to provide a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a circuit board ground plane and a chip. It is also desired to provide a chip mounting arrangement less vulnerable to damage due to handling than a surface mounted chip. It is further desired to provide a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a microstrip line board ground plane and a chip. It is yet further desired to provide a method of fabricating a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a circuit board ground plane and a chip.
An integrated circuit device includes a semiconductor chip, a circuit board and a layer of bonding material. The semiconductor chip has a surface plated with gold or another metal backing (e.g., aluminum or silver) on a first side and has a predetermined thickness. The circuit board has a first dielectric layer formed of dielectric material. The circuit board has a first conductive layer formed of electrically conductive material and bonded to a first side of the first dielectric layer and defining a plurality of conducting elements. The circuit board has a second conductive layer defining a first electrical ground plane formed of electrically conductive material and bonded to a second side of the first dielectric layer opposite the first conductive layer. The circuit board has a pocket formed therein. The pocket passes through the first conductive layer and through the first dielectric layer. The pocket is open on the first side. The pocket is closed on the second side by the second conductive layer. A portion of the second conductive layer is exposed at a bottom of the pocket. The pocket is of substantially the same size and shape as the semiconductor chip. The pocket receives the semiconductor chip with the first side of the semiconductor chip disposed toward the second conductive layer. The layer of bonding material is disposed in the pocket between the metal plated surface of the semiconductor chip and the second conductive layer. The layer of bonding material mechanically and electrically connects the semiconductor chip to the second conductive layer.
An integrated circuit device includes a semiconductor chip and a microstrip board and a layer of bonding material joining the chip and the microstrip board. The semiconductor chip has a surface plated with gold or another metal backing on a first side and has a predetermined thickness. The microstrip line board has a first dielectric layer formed of dielectric material. A first transmission layer is formed of electrically conductive material and is bonded to a first side of the first dielectric layer. The first transmission layer defines a plurality of conducting elements including a microstrip transmission line and a plurality of adjacent ground lines. A first ground plane layer is formed of electrically conductive material and is bonded to a second side of the first layer. The first ground plane layer defines a first electrical ground plane and is electrically connected to the ground lines by a plurality of vias extending from the first ground plane to the ground lines. The board has a pocket formed therein passing through the first transmission layer and through the first dielectric layer. The pocket is open on the first side and is closed on the second side by the first ground plane layer. A portion of the ground plane layer is exposed at a bottom of the pocket. The pocket is of substantially the same size and shape as the semiconductor chip. The pocket receives the semiconductor chip with the first side of the semiconductor chip disposed toward the ground plane layer. The layer of bonding material is disposed in the pocket between the metal surface of the semiconductor chip and the first ground layer. The layer of bonding material mechanically and electrically connects the semiconductor chip to the first ground layer.
A method of fabricating a semiconductor device includes the following steps. A semiconductor integrated circuit chip is formed, having a gold or other metal surface on one side thereof. A first substantially planar double sided laminate is formed, having a first dielectric layer formed of dielectric material and having a first conductive layer bonded to a first side of the dielectric layer and having a second conductive layer bonded to a second side of the dielectric layer opposite the first side. Portions of the first conductive layer are removed by etching the first conductive layer to define a plurality of discrete conducting elements. A predetermined amount of the first dielectric layer is removed to define a pocket therein of approximately the same size and shape as the integrated circuit chip. The pocket extends through the first conductive layer and through the first dielectric layer. The pocket is closed on the second side by the second conductive layer. Exposed surfaces of the first conductive layer and of a portion of the second conductive layer exposed inside of the pocket are plasma etched to clean the exposed surfaces. The surfaces cleaned by plasma etching are plated with gold or another metal. The metal layer of the integrated circuit is mechanically and electrically connected to a metal plated surface at an end of the pocket with a conductive bonding material.
The invention provides a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a circuit board ground plane and a chip. The invention also provides a chip mounting arrangement less vulnerable to damage due to handling than a surface mounted chip. The invention further provides a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a microstrip line board ground plane and a chip. The invention yet further provides a method of fabricating a semiconductor device which in turn provides a consistently reliable ground to chip connection at high frequencies between a circuit board ground plane and a chip.